Method for extending useful life of filter aid in a filter with hydraulically deformable system

ABSTRACT

A device for filtering fluid includes a hollow housing having a fluid inlet and a fluid outlet. A filter element formed of fluid permeable material is disposed within the housing for filtering fluid entering the fluid inlets, the fluid passing through the element and out the fluid outlet. The element has a generally cylindrical configuration with the permeable material forming a plurality of elongated, radially extending pleats. The pleats are supported by spacers having a plurality of blades attached to a web with channels therebetween. The element is used as a septum for supporting a diatomaceous earth precoat. A regeneration piston creates fluid flows within the filter that cause the element to flutter, thereby displacing DE precoat from the septum for regeneration.

This is a Divisional of application Ser. No. 08/456,156, filed May 31,1995 now U.S. Pat. No. 5,591,329.

FIELD OF THE INVENTION

The present invention relates to fluid filtering devices, and moreparticularly to diatomaceous earth filters employing a septum.

BACKGROUND OF THE INVENTION

Various fluid filtering devices have been proposed over the years, themore common types employing a porous filter media which is penetrable tothe fluid to be filtered but substantially impenetrable to contaminantsto be filtered out. A flow of fluid is directed through the media suchthat contaminant particles which do not pass through the pores of thefilter media are retained on or in the media on the upstream side.Purified fluid passes through the media and on to its end usedownstream. The pore size of the media determines the fineness offiltration or, conversely, the size of the contaminant particles whichpass through the media and are not filtered out. After a period offiltration, contaminants collected on the upstream side of the mediaplug or clog the media such that fluid flow through the media is reducedand/or the pressure differential between the fluid on the upstream sideof the media and the fluid on the downstream side is increased to anunacceptable level. Decreased flow translates to a reduction in purifiedfluid output, whereas an increase in differential pressure generallysignifies greater strain on the fluid systems producing the fluid flowto the filter, such as pumps, piping and seals, accelerating their wearand consuming more energy. For this reason, fluid filtration systemstypically have some provision for unclogging the filter media at regularintervals. This may take the form, inter alia, of reverse flushing themedia to waste, replacing the media with new media, subjecting the mediato some form of mechanical cleaning process such as scraping orbrushing, or a combination of the foregoing methods, depending upon themedia employed.

There are numerous kinds of filter media, with each type having itsadvantages and disadvantages with respect to filtering efficiency,backwashing/cleaning effectiveness and cost. For example, cartridgefilters typically employ a filter element fabricated from a fibrous orwoven sheeting material, such as a paper, felt, fiberglass, woven fabricor screen-like material surrounding a central, perforated core cylinderand capped with end plates. Cartridge filters are light in weight,compact and effective at removing small particulates. Fluid flow iscommonly directed from the outside of the cartridge element, whichusually approximates a cylindrical shape, to an inside core cylinder.The fluid permeable sheeting typically serves as the filter media itselfand may be backflushable. In order to increase the filter media surfacearea, it is known to fold the media sheet in a continuous zig-zag oraccordion pattern. Cartridge filters have certain inherent drawbacks,such as becoming clogged by fine particulates or organics that resistbackflushing. Cartridges also tend to collapse as the flexible mediasheet experiences greater pressure differentials. This collapse may takethe form of a general deformation of the overall cylindrical shape ofthe cartridge or the collapse of the peripheral folded zig-zag patternsuch that the surface area advantage provided by the folding isdefeated. Cartridge collapse has been remedied in the past by theinclusion of a parallel metal screening bent in the same shape as themedia sheeting. Solutions for the latter problem of the pinching down ofthe folds have been proposed in the form of corrugated fold separatorsmade from rigid plastics as shown, e.g., in U.S. Pat. Nos. 4,075,106 toYamazaki and 4,560,477 to Moldow. Because cartridge media becomesblocked under certain circumstances, the only remedy to restore themedia is replacement, which is both expensive and inconvenient, in thatthe cartridges are the products of rather complex fabrication methodsand to replace them, the filter must be disassembled.

As an alternative to filtering media in the form of woven or flockedsheeting, many filtering systems use a granular or particulate media,such as sand or diatomaceous earth, hereinafter "DE", as the primarymedia for collecting contaminants. The primary media is prevented fromentering the fluid flow by an element which is porous to the fluid to befiltered yet impenetrable to the granular media, e.g., a fine meshscreen or a sintered filter block. The granular media collects thecontaminants from the fluid stream thereby protecting themedia-impenetrable element from becoming clogged by contaminants. Thatis, the fluid to be filtered passes through a filter bed or cake ofgranular media and then through the media-impenetrable element, on toits final use downstream. For example, a DE filter typically contains atleast one septum which is a porous, fabric-like element that ispenetrable to the fluid to be filtered but not to DE. The septum haspores with dimensions which preclude the DE from entering the filterstream in significant amounts after a precoating of DE has beendeposited thereon. Usually, the pore size of the septum is larger thanthe particle size of the DE to promote flow and to insure that thefinest filtration takes place in the DE precoat. Even though the primarymedia has particles which are smaller than the septum pores,unacceptable leakage of primary media through the septum is avoided dueto the interlocking and agglomeration of DE particles to form groupswhich are larger than the pores in the septum. In this manner, the DEprecoating or filter cake protects the fine pores of the septum fromblockage by dirt. It is therefore desirable, for any given grade of DE,that the septum holes be significantly larger than the DE particle size.Septum pores that are too large however, result in unacceptable leakageof DE past the septum and prolonged periods of time for establishing aprecoat. DE is deposited upon the septum by introducing it into thefluid stream, typically in a slurry, such that it is deposited upon theseptum by fluid flow therethrough forming a filter cake or layer of DELon the septum. The septums of DE filters may take various forms and arefrequently disposed about a spacer of some sort which internallysupports the septum as e.g., shown in U.S. Pat. Nos. 3,774,772 to Yeths(arcuately-shaped), and 3,100,190 to Hobson, Jr. (tube-shaped).

The use of granular filter media like DE and sand has certain benefits,e.g., both are relatively inexpensive materials and tend to pack quiteclosely giving fine filtration results. As with all filters, however,after a period of use, contaminants and dirt accumulate on the upstreamside of the granular filter media. Granular media typically has a rangeof particle sizes and shapes, thus giving rise to a spectrum of poresizes in any given sample. Smaller dirt particles have a greatertendency to penetrate the surface of the granular media bed or cakeuntil being trapped by a smaller pore below the surface. This gives riseto a contaminated band of media extending from the surface into thedepth of the media. Eventually, the accumulation of dirt causes aresistance to flow and an increase in operating pressure indicating aneed to change the filter media or to clean the accumulated dirttherefrom in order to permit a resumption of normal flow rates. A commonmethod for cleaning dirt from DE filters is by backwashing, wherein areverse flow of fluid is directed through the septum to dislodgeaccumulated dirt, as well as, the DE filter cake from the septum. Thereverse backflushing flow, with dirt and DE filter media included, isdirected to waste, such that there is a loss of fluid and DE associatedwith a removal of dirt from the filter. In this day of ever increasingeco-consciousness, the disposal of DE in the course of backflushingfilters, e.g., on swimming pools, has received increased negativescrutiny.

As an alternative to backflushing, it has been recognized that the DEfilter media may be given extended filtering life by reorienting thefilter cake on the septum without backflushing or disposing of the DE.For example, U.S. Pat. No. 5,013,461 to Drori discloses a DE filter witha centrally located piston for creating reverse flows for dislodging DEfilter cake from the exterior surface of a laminated disk filterelement. Similar piston arrangements are shown in U.S. Pat. Nos.4,156,651 to Mehoudar and 1,994,656 to Liddell. U.S. Pat. No. 3,735,872to Anderson discloses apparatus for regenerating the DE precoat usingthe resiliency of foam septum elements underlying the precoat, byscraping and by classifying the dislodged DE into a precoat of graduatedparticles. Even without the affirmative step of classifying,reorienting, "opens up" the filter cake by breaking up the surfacecoating of dirt that clogs the DE filter cake. Reorienting disperses thedirt throughout the DE layer taking advantage of the improbability thatthe filter cake and dirt will reassume an orientation of particlespacked so closely together as to unduly restrict fluid flowtherethrough. The step of reorienting the DE without backflushinginvolves a cessation of filter operation, disturbing the DE filter cakeand filtered dirt from the septum in some manner, and resuming filteringoperation, such that the DE and the dirt are redeposited upon the septumin a new orientation. Reorientation will typically result in someportion of the DE and some portion of fine dirt which is smaller thanthe pores in the septum being introduced into the filtered fluid streamunless the fluid flow is directed to waste upon restarting.

Another limitation associated with DE filters is the tendency for the DEto coat the septum unevenly, wherein some portions are not coatedsufficiently and other portions are coated excessively. This is due tothe "bridging" of DE between adjacent surfaces of the filter element or"drifting" of the DE, creating areas of the septum where a thickimpervious layer of DE has been deposited due to the septum shape andits interaction with the hydrodynamic flows within the filter.

It is therefore an object of the present invention to provide animproved fluid filter having an element which exhibits an increasedfiltering surface area that is resistant to collapse or reduction offilter surface area under high differential pressures. It is a furtherobject to provide a diatomaceous earth filter which avoids bridging andis provided with apparatus to regenerate the DE precoat withoutbackwashing.

SUMMARY OF THE INVENTION

The problems and disadvantages associated with the conventionaltechniques and devices utilized to filter fluids are overcome by thepresent invention which includes a hollow housing having a fluid inletand a fluid outlet. A filter element formed of fluid permeable materialis disposed within the housing for filtering fluid entering said fluidinlet, the fluid passes through the element and out the fluid outlet.The element has a generally cylindrical configuration with the permeablematerial forming a plurality of elongated, radially extending pleats.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the present invention, reference is madeto the following detailed description of an exemplary embodimentconsidered in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a filter in accordance with an exemplaryembodiment of the present invention,

FIG. 2 is a cross-sectional view of the filter shown in FIG. 1, takenalong section line II--II and looking in the direction of the arrows,

FIG. 3 is a bottom, plan view of the flow deflector portion of thefilter shown in FIG. 2,

FIG. 4 is an exploded, perspective view of the filter element of thefilter shown in FIG. 2,

FIG. 5 is an elevational, end-on view of a septum spacer shown in FIG.4,

FIG. 6 is a cross-sectional view of the spacer of FIG. 5 taken alongsection line VI--VI and looking in the direction of the arrows,

FIG. 7A is a plan view of the filter element septum shown in FIG. 4,

FIGS. 7B and 7C are alternative embodiments of the septum shown in FIG.7A,

FIG. 8 is an elevational view of the piston knob locking flange of thefilter shown in FIG. 2,

FIG. 9 is a diagrammatic, plan view of a segment of a prior artcartridge filter element configuration precoated with diatomaceousearth,

FIG. 10 is a diagrammatic, plan view of a segment of a filter elementseptum configuration in accordance with the present invention andprecoated with diatomaceous earth,

FIG. 11 is an enlarged, diagrammatic view of the media regeneratorpiston of the filter of FIG. 2, in operation and producing local flowsof fluid through, and displacement of, the septum of the filter elementof the present invention, and

FIGS. 12A and 12B are diagrammatic views of the media regenerator pistonof the filter of FIG. 2 in operation during an upstroke and downstroke,respectively, and producing flows of fluid through the filter element ofthe present invention and through the inlet and outlet of the filter.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1 shows a filter 10 in accordance with the present invention havinga head portion 12 and a body portion 14. An internally threaded lockring 16 coacts with threads provided on the upper end of the bodyportion 14 to draw the head portion 12 into secure, water-tightengagement therewith. The lock ring 16 is knurled or molded with agripping surface and is provided with gripping tabs 18 to facilitaterotating the ring 16 by hand. A stationary gripping tab 20 projects fromthe body portion 14 to provide a solid fulcrum against which the hand ofthe user may be braced to exert pressure against the gripping tabs 18 ofthe lock ring 16. The gripping tabs 20, 18 on the body portion 14 andthe lock ring 16 are preferably located at those degrees of angulardisplacement of the ring 16 where the greatest resistance to turning isexperienced, i.e., at the point of final tightening and initialloosening.

A latch mount 22 protrudes from the body portion 14 for accommodatingthe insertion of a flexible shaft 24 functioning as a latch which isdisplaced by a ramp on the lock ring 16 until it overrides the rampedge, thereby locking the ring 16 in position such that it can not beunloosened by hydraulic pressure or vibration. To remove the lock ring16, the latch 24 may be displaced by bending it out of engagement withthe ramp extending from the lock ring 16. The latch mount 22 provides ahand grip against which a hand of the operator may be braced when thelock ring 16 is removed or installed. The filter 10 has an inlet port26, an outlet port 28 and a drain port 30. The body portion 14 has anintegral, bell-shaped base 32. A piston knob 34 at the top of the filter10 connects to a piston rod and piston for regenerating the filtermedia, as shall be described below. A conventional pressure gauge 36 andbleed valve 38 are also located on the top of the filter head 12. Thefilter body 14, head 12 and lock ring 16 may be formed from a toughplastic, such as polypropylene or ABS, in a conventional injectionmolding process.

FIG. 2 shows that the inlet port 26 discharges into a flow deflector 40having a one-way check valve 42. The flow deflector 40 redirects theinlet fluid stream downward into the hemispherical interior base surface44 of the filter. Fluid inflow fills the interior hollow of the filterfrom the base surface to the top interior surface 46 of the head portion12. On startup, the bleed valve 38 aids the discharge of air from thefilter system to admit fluid. The bleed valve 38 also facilitatesdraining the filter 10 of fluid for disassembly and cleaning. The flowdeflector 40 also serves as a bottom mounting hub 48 for the filterelement 50.

The head portion 12 has a raised annular upper mounting hub 52 coaxiallylocated relative to the bottom mounting hub 48, with a relative spacingtherebetween to sealingly receive and engage the filter element 50therebetween when the head portion 12 is fully engaged with the bodyportion 14 by the action of the lock ring 16. As can be observed, thelock ring 16 is held upon the filter head 12 by a pair of flanges 54,56. The filter head 12 is shaped and sized to be slidably receivedwithin the upper opening of the filter body 14 in piston/cylinderfashion. When the head 12 is inserted into the body 14, the lock ring 16comes into engagement with the mating threads 58 of the body 14providing a means for the user to urge the sealing ring 60 down into thefilter body 14 in sealing engagement. The sealing ring 60 is deformedwhen the head 12 is urged into the body 14 such that it assumes an ovalcross-sectional shape, as depicted. The upper annular flange 54capturing the lock ring 16 assists in the removal of the head 12 fromthe body 14 via the action of the lock ring 16 against it, as the lockring 16 is unthreaded. The gradual threaded action of the lock ring 16therefor provides a controlled mechanical advantage to overcome thefrictional forces exerted by the head 12 and sealing ring 60 against thebody 14 in both installing and removing the head portion 12 of thefilter.

The upper interior surface 46 of the head portion 12 includes severalguide vanes 62 to assist in maintaining proper filter element 50orientation while installing the head 12 onto the body portion 14. Morespecifically, the tapered guide vanes 62 have sloped surfaces to guidethe filter element 50 into position as the head 12 is lowered onto thebody 14 without the need to visualize the element 50. The filter element50 can be seen to include a central core cylinder 64 having numerousperforations 66, a pair of end caps 68, 70 and a porous septum 72retained therebetween. The core cylinder 64 may be fabricated fromplastic, ceramic or metal and includes, in the embodiment depicted, aplurality of internal, integrally molded strengthening rings 74. Therings 74 also have a guidance function relative to the movement of thepiston 76, as described below. The end caps 68, 70 may similarly beformed from metal, rubber or plastic, but in the embodiment shown, areformed of a rubber, such as urethane. Urethane end caps 68, 70 are stiffenough to provide rigidity and strength to the filter element 50 whileproviding sufficient flexibility to form integral seals 78, 80 at thetop and bottom openings of the filter element 50 for sealing against themounting hubs 48, 52. The urethane end caps 68, 70 also provide aconvenient method for sealing the septum 72 to the end caps 68, 70,viz., the end caps 68, 70 are sequentially formed by injection into amold already containing the septum 72 and core cylinder 64, such thatthe urethane flows around the septum and core cylinder.

The septum 72 may be composed of a spun bonded polypropylene netting ormay be formed from any flexible woven fabric or screening such as, e.g.,polyester screening. Polypropylene is a particularly advantageousmaterial for forming the septum 72 in accordance with the presentinvention, due to its stiffness and smooth surface. The stiffness of thepolypropylene assists the septum in retaining its pleated configurationand in bridging the blades of the spacers 81, as described more fullybelow, as well as the space between pleats. The smooth surface of thepolypropylene facilitates DE regeneration, in that DE is more easilyremoved from a smooth surface than a rough one. Septum spacers 81 may beemployed to insure that the septum retains its shape under operatingconditions.

In filtration mode, fluid entering the inlet port 26 fills the annularspace between the filter element 50 and the interior of the filter 10.Fluid then passes through the filter element, i.e., the septum 72 andany precoat deposited thereon, e.g., DE, through the perforations 66 inthe core cylinder 64, up through the cylinder and out the outlet port28. For traditional backwashing, a reverse flow is induced, such that DEand dirt are washed from the outer surface of the septum 72 and out towaste, e.g., through drain port 30. In the embodiment depicted,provision is made for regenerating a DE precoat without backwashing. Apiston 76 disposed within the core cylinder 64 is affixed to a pistonrod 82 which extends through the filter head 12 and receives a pistonknob 34 to be gripped by the user when the piston 76 is actuated toregenerate the DE filter cake.

The piston knob 34 includes locking fingers 84 that extend downwardlyand inwardly to grip mating prominences on a locking flange 86 which isdescribed and illustrated more fully below in reference to FIG. 8. Thelocking fingers 84 of the piston knob 34 prevent the fluid pressurewithin the filter from causing the piston 76 to be pushed upwards,thereby undesirably effecting fluid filtering. The piston rod 82 issealed by a gland nut 88 and suitable packing. accumulator for energyduring the operation of the filter and should therefore be eliminated toprevent an uncontrolled release of pressure.

FIG. 4 shows the filter element 50 with perforated core cylinder 64,pleated septum 72 and vented end caps 68, 70. The vent holes 96 in theend caps 68, 70 are provided for filters using a precoat of granularfilter media, such as DE filters. In such embodiments, the vent holes 96are disposed between the pleats 98 of the septum 72, described morefully below, such that filter flow will be directed through the ventholes 96 to clear excess DE from between septum pleats 98 andeliminating drifting and bridging of DE between septum pleats. Bridgingis also reduced by the vent holes 96 due to the DE sloughing from theseptum 72 when the filter 10 is turned off. The vent holes 96 permit thefallen DE to drain through the end cap 70 from between the septumfingers 98 into the bottom of the filter 10. Upon resuming filtration,the sloughed DE is carried by the filtering flow of fluid to evenly coatthe septum 72.

FIG. 4 also shows septum pleat spacers 81 which are substantially rigidmembers that slide into the septum pleats 98 to allow them to retaintheir overall shape when subjected to the pressures of filtration andthe increased differential pressures associated with a cloggedcondition. The spacers 81 have a plurality of blades 102 and channels104 therebetween to channel fluid toward the core cylinder 64 to enablenormal fluid flow through the element 50. FIGS.

In the embodiment shown, the piston 76 has a diameter approximating thatof the internal stiffening rings 74 and a height somewhat greater thanthe spacing between adjacent rings 74. The strengthening ribs 92 of thepiston 76 have an inwardly inclined bevel, which, along with the heightof the piston 76, assure that it traverses the core cylinder's internalrings 74 without binding, by bridging from one internal ring 74 to thenext. In this manner, the piston is retained in the approximate centerof the core cylinder 64. The piston 76 has a stroke extending from thebottom stroke position shown, to a position where the top surface of thepiston 76 contacts the gland nut 88. As noted above, a pressure gauge 36and bleed valve 38 are provided.

FIG. 3 shows the flow deflector 40 from the bottom. As can beappreciated from this view, the flow deflector 40 does not partition thebottom portion of the body 14 into chambers, but instead, is more in thenature of a outlet around which fluid flow may take place. The roundmounting hub 48 is disposed in the approximate center of the flowdeflector. An air relief slot 94 provides a passageway for air to escapefrom the interior dome of the mounting hub 48 and bubble up into thefilter to be removed from the filter by bleed-off or passage through thefilter. This is a safety feature, in that air that is permitted toaccumulate in any pockets within the filter can serve as an 5 and 6illustrate a septum pleat spacer 81 which has a plurality of spacedblades 102 and channels 104 therebetween. The plan view shape of theblades 102 shown in FIG. 6 is equivalent to the plan view shape of theseptum pleat 98 shape. A web 106 extends between the blades 102.

FIGS. 7A through 7C show a three different embodiments for the septumpleat 98 shape. As can be appreciated from FIG. 7A, the septum 72includes a plurality of projections or pleats 98 emanating from thecenter and projecting radially outward. The pleats are formed by foldinga sheet of septum material and binding the loose ends together at theseam 108. In contrast to prior art corrugated cartridge filters, e.g.,as shown in FIG. 9, each pleat 98 in the present invention is separatedone from another by an intermediate portion or link 110 of septummaterial proximate the origin of the pleat 98 near the core of theseptum 72/element 50. In contrast, and as depicted in FIG. 9, the mediasheeting of prior art corrugated filter elements converge to a sharpedge at the origin of each successive corrugation. If used as a DEfilter element septum, the convergence of the corrugations of prior artelements results in bridging and drifting of the DE into the convergingedges of the element. This results in an uneven coating of the septumwherein portions at the apogee of the corrugations are insufficientlycoated allowing contamination of the septum, and portions near theconverging inner edges that are too heavily coated, reducing fluid flow.

One might also observe that a septum shape in accordance with thepresent invention results in a smaller septum surface area than asimple, densely packed, zig-zag corrugation pattern for a givencylindrical volume of space for the element to occupy. This is due tothe elongated trapezoidal shape of the pleats 98, wherein the outer endof the pleat has a greater width than the inner end and to the spacingbetween pleats on the inner circumference of the element. Nevertheless,due to the avoidance of bridging effects, a precoated septum inaccordance with the present invention will have an equivalent or greatersurface area as compared to a simple corrugated element.

FIG. 7B shows an alternative embodiment which is essentially acombination of the box-shaped pleat 98 of the present invention with theconverging pleat edge of the traditional corrugated element design. Thisembodiment exhibits a tendency to experience bridging in the convergingedges of the pleats 98 when DE filter media is used.

FIG. 7C shows yet another pleat 98 shape in accordance with the presentinvention. This shape avoids the problem of bridging due to theinclusion of intermediate spaces 110 between the pleats at their basesproximate the core of the element.

FIG. 8 is an enlarged elevational view of the piston knob locking flange86 referred to above. The flange 86 has a plurality of slots 112 forreceiving the locking lingers 84 that project downwardly and inwardlyfrom the piston knob 34. The slots 112 terminating under flange segments113 having a lower face 114 which is approximately perpendicular to thedirection of piston rod 82 travel. As a result of this relativeorientation, upward pressure on the piston 76 translates into purecompressive forces by the fingers 84 of the locking knob 34 upon theflange segment lower faces 114 and there is no tendency for the fingers84 to slide relative to the flange segment lower faces 114 to unloosenthe knob 34 from its locked position. The lower face 114 may incorporatea raised pimple 116 to increase the frictional interaction between thelocking fingers 84 of the knob 34 and the flange 86 segments. Thelocking fingers 84 may also be provided with a raised pimple to engagepimple 116.

FIG. 9 shows the results of using a conventional corrugatedcartridge-type element E as a DE septum, viz., when the element E isprecoated with DE, there is a tendency for the DE to accumulate in thevalleys of the corrugations reducing fluid flow through these areas ofthe septum.

FIG. 10 illustrates a filter element 50 utilizing a septum 72 inaccordance with the present invention and coated with a DE precoat 118.Due to the link spaces 110 between successive pleats 98, DE bridging isavoided. One of the end caps 70 is also shown and includes a pluralityof vent holes 96 to promote fluid flow between the septum pleats 98.Flow between the pleats helps to prevent any accumulation of DE betweenthe pleats 98 or "bridging". The vents 96 in the bottom end cap 70 alsoserve as drain holes to permit DE to drain through the end cap 70sloughing off the element 50 when the filter 10 is turned off, ratherthan collecting on the bottom end cap 70 between the pleats 98 in a"snow bank". This promotes keeping the DE in suspension upon restarting,which results in a higher DE-to-dirt ratio in the precoat and a thicker,more even precoat.

FIG. 11 diagrammatically depicts some of the local fluid flows thatoccur upon activating the regeneration piston 76. More specifically,when the piston 76 is displaced upwardly, a low pressure area is createdbelow the piston 76. The low pressure induces a flow of fluid into thecore cylinder 64 from outside the element 50 and through the septum 72.This flow pushes the septum 72 against the core cylinder 64. Above thepiston 76, a high pressure condition is created, such that the fluid inthe cylinder 64 is urged out through the perforations 66, through theseptum 72 and out into the annular space surrounding the element 50.This flow pushes the septum 72 away from the core cylinder 64.

In addition to flows through the perforations 66 in the core cylinder64, there is also a flow within the core cylinder 64 through theclearance space between the cylinder 64 wall and the piston 76. Thisflow would be in the direction from the high pressure area above thepiston 76 to the low pressure area below the piston. Because there is anurging of the septum 72 toward the core cylinder 64 below the piston 76and an urging of the septum 72 away from the core cylinder 64 above thepiston 76, the septum 72 is rippled or bulged in the area of thistransition which occurs proximate the piston 76. This bulging orrippling follows the piston along its entire stroke. The return strokehas essentially the same effect and flows associated therewith, but withthe flow directions reversed, due to the reversal of high and lowpressure areas from one side of the piston 76 to the other.

Since the septum 72 is a deformable, resilient web or screen-like unit,ripples induced in the central portion thereof are transmitted radiallythroughout the entire septum. In this manner, the septum 72 can beobserved to ripple or flutter as a result of the actuation of theregeneration piston 76. The rippling of the septum 72 in conjunctionwith flows through the core cylinder perforations 66 and septum 72 in anoutward direction are effective in displacing DE precoating from theexterior surface of the septum, in that the coating is disturbed bothmechanically and hydraulically.

To regenerate the DE precoat, the filter pump is turned off to relievethe fluid pressure on the filter cake. The regenerator piston is thenactuated up and down to displace the DE from the septum. Uponrestarting, the DE reorients itself upon the septum. A puff of DE andfine dirt can be anticipated to enter the filtered fluid stream uponrestarting. If such fluid is to be recycled through the filter, theescaping puff will be filtered out in subsequent cycles. To avoid anescape puff from entering the fluid stream, the stream can betemporarily redirected back into the filter or to waste until theprecoat restabilizes.

FIGS. 12A and 12B are another illustration of fluid flows within thefilter 10 upon actuation of the regeneration piston 76. In 12A, thepiston 76 is urged upward creating a flow out of the core cylinder 64,through the element 50 and into the annular space surrounding theelement, as previously described. Below the piston 76, a low pressurearea draws fluid from the annular space through the element 50 and intothe core cylinder 64. As a result, an overall toroidal flow pattern iscreated. As noted above, there is also a flow around the piston 76through the clearance between the piston 76 and the core cylinder 64. Inaddition to the above-described flows generated within the filter byregeneration, there is also a flow of fluid out the filter outlet 28 dueto the pressure differential created by the piston 76 in the upper partof the filter 10. Low pressure in the bottom of the filter 10 inducesthe one way valve 42 to open, admitting fluid into the filter 10. Theinertia of the fluid in the outlet port 28 and inlet port 26 prevent thework of the piston from resulting purely in a displacement of fluid outthe outlet port 28.

FIG. 12B shows essentially the reverse flows of FIG. 12A, with theexception that the check valve 42 in the bottom of the filter 10 closeson the downstroke to prevent the loss of DE through the bottom inletport 26.

Regeneration of the DE precoat is very effective in extending the lifeof the DE, thereby preventing unnecessary disposal of DE. Afterprolonged use, however, dirt content in the filter may become excessive,requiring the disposal of the old precoat and the application of a newone. This operation may be conducted by draining the fluid, DE and dirtfrom the filter 10 through the drain 30. The filter head 12 may then bedisassembled from the body portion 14 by unfastening the ring 16 and thefilter element 50 cleaned by hosing it down. Alternatively, the septum72 may be subjected to a chemical bath to dissolve and dislodgecontaminants therefrom. The filter 10 is reassembled and a new precoatapplied.

It should be understood that the embodiments described herein are merelyexemplary and that a person skilled in the art may make many variationsand modifications without departing from the spirit and scope of theinvention as defined in the appended claims.

I claim:
 1. A method for increasing the service life of a diatomaceousearth precoat applied to a hydraulically deformable thin-walled septum,comprising the steps of:(a) inducing a first flow of fluid in a firstdirection through a first area of said septum; (b) inducing a secondflow of fluid in a second direction opposite to said first directionthrough a second area of said septum, said first and second flowshydraulically urging said septum in opposing directions thereby bendingsaid septum in a transition area located between said first area andsaid second area, said bending resulting in the rippling of said septumwhich, in turn, facilitates the displacement of said precoat from saidseptum; (c) moving the location of said first flow, said second flow andsaid transition area along a length of said septum such that saidrippling and said precoat displacement occurs along said length of saidseptum; and (d) reapplying at least some of said precoat to said septum.2. The method of claim 1, wherein said length of said septum along whichsaid rippling occurs is substantially the entire length of said septum.3. The method of claim 1, further including the step of reversing thedirection of moving said location of flows such that the length of saidseptum is traversed in the opposite direction with said first and saidsecond flows being reversed in direction.
 4. The method of claim 3,wherein said steps of inducing said first and second flows are performedby a fluid displacement apparatus.
 5. The method of claim 4, whereinsaid fluid displacement apparatus is a piston traversing a porouscylinder disposed in and containing said fluid.
 6. The method of claim5, wherein said piston is reciprocable within said cylinder, said firstflow attributable to displacement of said fluid ahead of said piston onthe upstroke, said second flow attributable to said fluid entering saidcylinder behind said piston on the upstroke, said step of reversingattributable to the reversal of the direction of said piston direction.7. The method of claim 5, wherein said piston generates a third flow offluid from a leading side of said piston to a trailing side thereofthrough a clearance between said piston and said cylinder when saidpiston is moved in said cylinder.
 8. The method of claim 7, wherein saidthird flow is partially vented through said cylinder proximate saidpiston, said vented third flow billowing said septum proximate saidpiston.
 9. The method of claim 1, further including spacer means forsupporting said septum internally, said septum being loosely fittedaround said spacer means such that said septum is free to ripple underthe influence of said first flow and said second flow.
 10. The method ofclaim 9, wherein said septum is pleated and roughly conforms in shape toan outer peripheral surface of said spacer means.
 11. The method ofclaim 10, wherein said septum is made from spun bonded polypropylene.12. The method of claim 10, wherein said septum is made from a wovenfabric.
 13. The method of claim 10, wherein said septum is made frompolyester screening.